Hitherto, as polymers that have relatively low molecular weight and crystallinity and are usable as hot-melt adhesives, etc., there are known propylene homopolymers or olefin-based polymers produced by copolymerizing propylene with ethylene or 1-butene.
However, these polymers are deteriorated in uniformity due to broad molecular weight distribution and broad composition distribution thereof.
Meanwhile, conventionally, 1-butene polymers have been produced using magnesium-supported titanium catalysts (Japanese Patent Application Laid-Open No. Hei 7-145205). However, the thus produced 1-butene polymers have a non-uniform composition which, therefore, gives adverse influences on properties thereof such as occurrence of stickiness and poor transparency.
In this regard, in recent years, 1-butene polymers having a uniform composition have been produced using metallocene catalysts (Japanese Patent Application Laid-Open Nos. Sho 62-119214, Sho 62-121708, Sho 62-121707, Sho 62-119213 and Hei 8-225605).
In addition, Japanese Patent Application Laid-Open No. Sho 63-57615 discloses high-fluidity 1-butene-based polymers.
However, in any of these conventional methods, since non-crosslinked metallocene catalysts are used therein, the obtained polymers are liquid amorphous 1-butene-based polymers. Therefore, these 1-butene-based polymers have problems concerning poor surface properties, etc.
Also, hot-melt adhesives used in hot-melt bonding methods in which high-molecular compounds are heat-melted and bonded together, have been extensively employed in various applications because they are excellent in high-speed coatability, rapid curability, solvent-free applicability, barrier property, energy-saving property, inexpensiveness, etc.
The conventional hot-melt adhesives are mainly composed of resins prepared by blending a tackifier resin or a plasticizer in a base polymer such as natural rubbers, ethylene-vinyl acetate copolymers, styrene-butadiene-styrene block copolymers and styrene-isoprene-styrene block copolymers.
However, since the above base polymers contain a large amount of double bonds, the hot-melt adhesives produced using such base polymers exhibit a poor thermal stability upon heating and, therefore, suffer from oxidation, gelation, decomposition and discoloration upon coating. In addition, there occurs such a problem that portions bonded by the hot-melt adhesives are deteriorated in strength with time.
Further, the hot-melt adhesives are also deteriorated in adhesion to low-polar substances such as polyethylene and polypropylene.
To solve the deteriorated adhesion to the low-polar substances, there have been conventionally known hot-melt adhesive resins containing propylene as a base polymer. Although these resins show an excellent thermal stability, the base polymer contained therein has a too high hardness and is deteriorated in fluidity. As a result, the hot-melt adhesive resins must be applied under a high temperature condition, so that there occurs such a problem that the thermal stability of the resins becomes lowered under such a high-temperature condition and, therefore, a sufficient adhesion strength cannot be attained.
In this regard, as described above, it is known that propylene homopolymers as well as olefin-based polymers having relatively low molecular weight and crystallinity which are produced by copolymerizing propylene with ethylene or 1-butene, are usable as the base polymer for the hot-melt adhesives (Japanese Patent Application Laid-Open No. Hei 7-145205).
These polymers are excellent in balance between fluidity, flexibility and fabricability, but deteriorated in tenacity. Therefore, when these polymers are used as an adhesive between an elastomer and a nonwoven fabric, there arises such a problem that the resultant product is deteriorated in adhesion strength.
For example, there is known the method using low-crystalline polymers which are enhanced in tenacity by reducing a stereoregularity thereof (Japanese Patent Application Laid-Open No. 2002-322213). However, when the stereoregularity of the polymers is excessively reduced, crystallized portions serving as physical crosslinking points are insufficient, which rather results in deteriorated tenacity of the polymers.
On the other hand, when the molecular weight of the polymers increases to allow the polymers to be entangled with each other and thereby attain a good tenacity, the resultant polymers exhibit a high tenacity, but tend to be deteriorated in fluidity.
Thus, in the conventional hot-melt adhesives, it has been required to control the balance between fluidity and tenacity of the base polymer used therein.
The present invention has been completed to solve the above conventional problems. An object of the present invention is to provide a 1-butene-based polymer having a uniform composition, a well-controlled stereoregularity, a high fluidity and a high flexibility, a process for producing the 1-butene-based polymer, and a resin modifier made of the 1-butene-based polymer.
A further object of the present invention is to solve the problems as to poor tenacity of the base polymer used in the conventional hot-melt adhesives, and provide a hot-melt adhesive containing the 1-butene-based polymer which is excellent in not only balance between fluidity and tenacity, thermal stability under a high temperature condition, and adhesion to low-polar substances, but also heat resistance at the bonded surface.